Field of the Invention
This invention relates generally to protein purification. In particular, the invention relates to a method for purifying antibody from a composition comprising the antibody and at least one contaminant using cation exchange chromatography, wherein a high pH wash step is used to remove contaminants prior to eluting the desired antibody using an elution buffer with increased conductivity.
Description of the Related Art
The large-scale, economic purification of proteins is an increasingly important problem for the biotechnology industry. Generally, proteins are produced by cell culture, using either eukaryotic or prokaryotic cell lines engineered to produce the protein of interest by insertion of a recombinant plasmid containing the gene for that protein. Since the cells typically used are living organisms, they must be fed with a complex growth medium, containing sugars, amino acids, and growth factors, usually supplied from preparations of animal serum. Separation of the desired protein from the mixture of compounds fed to the cells and from the by-products of the cells themselves to a purity sufficient for use as a human therapeutic poses a formidable challenge.
Procedures for purification of proteins from cell debris initially depend on the site of expression of the protein. Some proteins can be cased to be secreted directly from the cell into the surrounding growth media; others are made intracellularly. For the latter proteins, the first step of a purification process involves lysis of the cell, which can be done by a variety of methods, including mechanical shear, osmotic shock, or enzymatic treatments. Such disruption releases the entire contents of the cell into the homogenate, and in addition produces subcellular fragments that are difficult to remove due to their small size. These are generally removed by differential centrifugation or by filtration. The same problem arises, although on a smaller scale, with directly secreted proteins due to the natural death of cells and release of intracellular host cell proteins in the course of the protein production run.
Once a clarified solution containing the protein of interest has been obtained, its separation from the other proteins produced by the cell is usually attempted using a combination of different chromatography techniques. These techniques separate mixtures of proteins on the basis of their charge, degree of hydrophobicity, or size. Several different chromatography resins are available for each of these techniques, allowing accurate tailoring of the purification scheme to the particular protein involved. The essence of each of these separation methods is that proteins can be caused either to move at different rates down a long column, achieving a physical separation that increases as they pass further down the column, or to adhere selectively to the separation medium, being then differentially eluted by different solvents. In some cases, the desired protein is separated from impurities when the impurities specifically adhere to the column, and the protein of interest does not, that is, the protein of interest is present in the “flow-through”.
Ion exchange chromatography is a chromatographic technique that is commonly used for the purification of proteins. In ion exchange chromatography, charged patches on the surface of the solute are attracted by opposite charges attached to a chromatography matrix, provided the ionic strength of the surrounding buffer is low. Elution is generally achieved by increasing the ionic strength (i.e. conductivity) of the buffer to compete with the solute for the charged sites of the ion exchange matrix. Changing the pH and thereby altering the charge of the solute is another way to achieve elution of the solute. The change in conductivity or pH may be gradual (gradient elution) or stepwise (step elution). In the past, these changes have been progressive; i.e., the pH or conductivity is increased or decreased in a single direction
U.S. Pat. Nos. 6,339,142, 6,417,355, 6,489,447, and 7,074,404 (Basey et al.) describe ion exchange chromatography for purifying polypeptides. U.S. Pat. Nos. 6,127,526, 6,333,398, and 6,797,814 (Blank, G.) describe purifying proteins, such as anti-HER2 antibodies, by Protein A chromatography. Methods for purifying proteins, such as antibodies, by ion exchange chromatography are described in US Application Publication No. 2004/0082047.
U.S. Pat. No. 5,110,913 refers to purifying an antibody in an aqueous solution by binding the antibody to an ion exchange resin at a first pH of 4.6, washing at a second pH of 5.5, and eluting the antibody at pH 6.5, wherein the ionic strength of the solutions of these three steps remains constant. Zhang et al. refer to Q membrane, anion exchange chromatography of a human antibody (Zhang et al. “Q Membrane Chromatography Application for Human Antibody Purification Process,” Poster presented at BioProduction, October 26-27, 2004 Munich, Germany). Other publications concerning protein purification include: Barnthouse et al. J. Biotech. 66: 125-136 (1998); Blank et al. Bioseparation 10: 65-71 (2001); Follman and Fahrner J. Chromatog. 1024: 79-85 (2004); Iyer et al. BioPharm 15(1):14-16, 18, 20, 53 (2002); US 2004/0082047A1; EP 333,574; EP 460,426 B1; EP 556,083; WO 89/05157; WO 92/22653; WO 93/06217; WO 95/22389; WO 96/33208; WO 96/40883; U.S. Pat. No. 4,753,894; U.S. Pat. No. 4,966,851; U.S. Pat. No. 5,110,913; U.S. Pat. No. 5,112,951; U.S. Pat. No. 5,115,101; U.S. Pat. No. 5,118,796; U.S. Pat. No. 5,169,774; U.S. Pat. No. 5,196,323; U.S. Pat. No. 5,256,769; U.S. Pat. No. 5,279,823; U.S. Pat. No. 5,429,746; U.S. Pat. No. 5,451,662; U.S. Pat. No. 5,525,338; U.S. Pat. No. 5,677,171; U.S. Pat. No. 6,005,081; U.S. Pat. No. 6,054,561; U.S. Pat. No. 6,127,526; U.S. Pat. No. 6,267,958; U.S. Pat. No. 6,339,142; U.S. Pat. No. 6,417,335; U.S. Pat. No. 6,489,447; Adachi et al., Journal of Chromatography. A. 763(1-2):57-63 (Feb. 28, 1997); Gagnon, P., Purification Tools for Monoclonal Antibodies, Tucson:Validated Biosystems, Inc., Chapter 4, pps. 57-86 (1996); Graf et al., Bioseparation 4(1):7-20 (February 1994); Mhatre et al., Journal of Chromatography A 707(2):225-231 (Jul. 21, 1995); Neidhardt et al., Journal of Chromatography 590(2):255-261 (1992); Protein Purification Applications—A Practical Approach, Harris and Angal, IRL Press pps. 151-156 (1995); Sofer et al. Handbook of Process Chromatography: A Guide to Optimization, Scale-up, and Validation, San Diego:Academic Press pps. 65-80 (1997); Tishchenko et al., Journal of Chromatography B 706(1):157-166 (Feb. 27, 1998).